1. Field of the Invention
The present invention relates to an image forming apparatus, a method thereof, and a computer program product.
2. Description of the Related Art
In apparatuses such as a copying machine and a multifunction peripheral (MFP) that houses a plurality of functions such as copy, facsimile, and printer functions in one housing, image adjustments such as a color shift correction and a density correction are performed by forming test patterns on an intermediate transfer belt with a toner, and then by detecting the test patterns with a plurality of sensors. The sensors detecting the test patterns are placed at locations at which main-scanning positions of the sensors are different from each other, and the test patterns are formed at locations on the intermediate transfer belt where the sensors can detect the test patterns.
In addition, in order to reduce time (down time) during which a printing operation cannot be performed due to the image adjustment, the image adjustment is performed by forming the test patterns at both ends outside a main-scanning image area concurrently with the printing operation.
However, in the above-described method in which the test patterns are formed at both ends outside the main-scanning image area concurrently with the printing operation, the sensors for detecting the test patterns need to be placed at outer ends of the image area. In addition, in the case of forming test patterns having a large width in a main-scanning direction, a laser diode (LD) needs to emit light outside an optical properties guarantee area of an LD scanning optical system. Thus, there is a problem that operational trouble or image degradation is caused by, for example, exposure of an unintended place to flare light.
Here, the term “optical properties guarantee area” refers to an area in a main-scanning direction in which a scanning beam is guaranteed to be emitted to a target area of a photosensitive element. Outside this area, lens properties of the scanning optical system are not guaranteed, and when the beam is turned on, exposure of an unintended place occurs. When the unintended exposure occurs in the photosensitive element, the exposure causes occurrence of troubles such as a failure in an adjusting operation and image degradation, or, when the unintended exposure occurs in a sensor such as a synchronization detector, the exposure causes occurrence of operational abnormalities.
In order to reduce the down time due to the image quality adjustment, Japanese Patent Application Laid-open No. 2009-169031 discloses a method in which patterns are formed for sensors at the ends of the image. Furthermore, in order to detect patterns for detecting a positional deviation without fail, Japanese Patent Application Laid-open No. H11-102098 discloses a method in which a rough adjustment is first performed by roughly making correction with large shaped patterns, and then a fine adjustment is performed by finely making correction with small shaped patterns.
However, the technique described in Japanese Patent Application Laid-open No. 2009-169031 merely forms the patterns at the outer ends of the image area at the same time when the image is formed, and does not form patterns for sensors inside the image area. Thus, the patterns formed for the sensors at the ends of the image are situated outside the optical properties guarantee area. That is, a light source emits light outside the optical properties guarantee area. In the technique described in Japanese Patent Application Laid-open No. H11-102098, too, the light source emits light outside the optical properties guarantee area, depending on the size of the patterns formed and the locations of the sensors.
Therefore, there is a need for an image forming apparatus and a method thereof that are capable of suppressing the light source from emitting light outside the optical properties guarantee area.